Arnold Walfisz (2 July 1892 – 29 May 1962) was a Jewish-Polish[1] mathematician working in analytic number theory.

After the Abitur in Warsaw, Poland, Arnold Walfisz studied (1909−14 and 1918−21) in Germany at Munich, Berlin, Heidelberg and Göttingen.

Walfisz lived in Wiesbaden from 1922 through 1927, then he returned to Warsaw, worked at an insurance company and at the mathematical institute of the university (habilitation in 1930).

In 1935, together with Salomon Lubelski [pl], he founded the mathematical journal Acta Arithmetica.

By using a theorem by Carl Ludwig Siegel providing an upper bound for the real zeros (see Siegel zero) of Dirichlet L-functions formed with real non-principal characters, Walfisz obtained the Siegel–Walfisz theorem, from which the prime number theorem for arithmetic progressions can be deduced.